large numbers in log space -- dividing summations

Hi, I originally posted this is Calculus (it was my first post, probably a mistake, maybe still a mistake to post here, I am not sure). I tried to get help in Chat, but it wasn't coming up, and I tried to post in the Questions/Comments section, but I wasn't allowed. So, I realize I am somewhat double posting here, so I apologize.

Re: large numbers in log space -- dividing summations

Originally Posted by timfoea

Hi, I originally posted this is Calculus (it was my first post, probably a mistake, maybe still a mistake to post here, I am not sure). I tried to get help in Chat, but it wasn't coming up, and I tried to post in the Questions/Comments section, but I wasn't allowed. So, I realize I am somewhat double posting here, so I apologize.

Re: large numbers in log space -- dividing summations

where a,b,c are very large constants, (e.g., a = 10000, b = 20000, c = 30000), and I step the summations by, say, 0.01

thus, i use log space so this is tractable on a computer:

the problem is that in order to do the final division, i have to take where n is a very small number for both the numerator and denominator, and thus the computer considers this to be 0. I would like to be able to do the all the math in log space before having to come out of it with

Does that make sense?

Last edited by timfoea; August 11th 2011 at 01:03 PM.
Reason: step info

Re: large numbers in log space -- dividing summations

where a,b,c are very large constants, (e.g., a = 10000, b = 20000, c = 30000), and I step the summations by, say, 0.01

thus, i use log space so this is tractable on a computer:

the problem is that in order to do the final division, i have to take where n is a very small number for both the numerator and denominator, and thus the computer considers this to be 0. I would like to be able to do the all the math in log space before having to come out of it with

Does that make sense?

For "very large":

That is all the terms in the summation are negligable compared to the largest.

But I doubt that what you posted is the real question, which is what you should have posted.